1. Field of the Invention
The present invention concerns a regulating member for a wristwatch, and a timepiece for a wristwatch comprising such a movement.
2. Description of the Prior Art
Usual mechanical watches comprise an energy accumulator constituted by a barrel, a kinematic chain, or gear-train, driving hands, a regulating member determining the working of the watch as well as an escapement for transmitting the oscillations of the regulating member to the gear-train. The present invention concerns in particular the regulating member.
The regulating members of conventional mechanical watches most often include a balance mounted on a rotation axis and a return member exerting a torque on the balance to bring it back towards a resting position. The escapement maintains the oscillations of the balance around the resting position. The return member generally includes a spring, the spiral or hairspring, which transmits a restoring torque to the balance through the collet.
The oscillator formed by the balance-hairspring pair offers remarkable properties for measuring time. It has however the disadvantage of being sensitive to gravity, which tends to deform the hairspring differently depending on the watch's tilt. Furthermore, the manufacture of the hairsprings is delicate and these elements are traditionally difficult to obtain.
Furthermore, electric watches are known whose working is regulated by an electromechanical oscillator comprising coils and magnets. For example, U.S. Pat. No. 4,266,291 describes an oscillating mechanism for a watchmaking application based on permanent magnets and requiring an electric power source to excite a stator with a pulsed current. GB1175550 describes a resonator having an H-shaped part provided with oscillating magnets in a magnetic field created by coils or electrostatic elements. The frequency of oscillation is determined by the geometry of the resonator.
By comparison to these documents, one aim of the present invention is notably to propose a regulating member that can also function in an entirely mechanical timepiece and without battery or other source of current.
On the other hand, CH615314 describes a regulating member with a balance and a hairspring conventional; the regularity of the oscillations is improved by means of a magnet mounted on a vibrating tab and vibrating in the magnetic field of a fixed magnet. In a similar manner, US2003/0137901 describes a mechanical watch comprising magnets for detecting or correcting the position of the balance; the frequency of the balance's oscillations is however determined by an ordinary hairspring. EP1122619 describes different embodiments of a mechanical watch whose balance is provided with magnets generating a magnetic field in fixed induction coils connected to the movement. The intensity of the current in the coils enables the amplitude of oscillation and thus the working of the watch to be controlled. It is also suggested to correct this function in the case of irregular oscillations. The movements of the balance are however stabilized by a hairspring and not by magnets.
Various documents further describe a magnetic escapement associated to a conventional regulating member. For example, U.S. Pat. No. 3,183,426 describes a magnetic escapement for watch movement. This device uses magnets placed on the balance. It is however not suggested to do away with or replace the hairspring.
Similarly, CH274901 describes various embodiments of mechanical escapements associated to a regulating member with conventional hairspring.
These different solutions thus require an additional magnetic system besides the spiral hairsprings. They thus have all the disadvantages connected to the spiral hairspring, whilst also adding further complexity. One aim of the present invention relative to these various solutions is thus to eliminate the spiral hairspring.
U.S. Pat. No. 3,877,215 describes a member comprising a tuning-fork whose vibrations are transmitted to the balance through magnetic coupling. GB1142676 describes another mechanical and magnetic oscillator with a tuning-fork. CH235718 describes a regulating member for a watch comprising a flexible oscillating rod whose extremity is provided with a magnet vibrating in the magnetic field of a fixed magnetic pole.
These solutions make it possible to eliminate the spiral hairspring but replace it by a tuning-fork whose elastic deformations determine the working of the watch. The manufacture of an accurate tuning-fork poses problems similar or even more complex than the manufacture of a high precision hairspring.
U.S. Pat. No. 3,621,424 describes a pendulum oscillating in a magnetic field caused by a single magnet connected to the escapement. The magnet thus serves both for the escapement and to bring the pendulum back to its position of equilibrium. The pendulum must however be subjected to the force of gravity and can only function in vertical position, i.e. in a clock.
U.S. Pat. No. 4,308,605 describes a regulating member for a timepiece provided with a vertical-axis balance. Magnets enable the gravitation force to be compensated in order to offset the pressure differences on the two bearings and limit the flexion of the staff of the balance wheel due to its own weight. A conventional hairspring controls the oscillations.
U.S. Pat. No. 5,638,340 concerns a table clock with an oscillating pendulum that is levitated in a magnetic field and which, in one embodiment, determines the working of the watch. The oscillating member is thus totally decoupled from the kinematic hands driving chain. This device however requires a source of electric energy to produce the levitation magnetic field and for the optoelectronic sensors servo-controlling the position of the pendulum. The mechanism is not adapted to a wristwatch.
GB615139 mentions a clock with vertical gravitational pendulum. The extremity of the pendulum oscillates along a circular trajectory controlled by magnets and thus drives the watch's movement.
By comparison with these four latter documents, one aim of the present invention is notably to propose a regulating member adapted to a wristwatch and whose function and working are practically independent of gravity and of the orientation of the regulating member relative to the vertical.
GB644948 describes a galvanometer with an inertial mass provided with two mobile magnets. A fixed permanent magnet generates a magnetic field enabling the balance to be brought back into its position of equilibrium. A conventional anchor escapement maintains the oscillations. This solution is only sketched in a schematic manner; magnets having a relatively large size are however necessary. These magnets generate a magnetic field all around the regulating member, which is likely to disturb the working of the device and to attract parts or members nearby.
Patent application WO2006/045824 in the name of the applicant, whose content is integrated herewith by way of reference, proposes to replace the spiral hairspring of the prior art by at least one permanent magnet that pushes the balance back towards its resting position against the escapement's pulses. The magnet's magnetic force is independent of its orientation in space and it is thus possible to avoid disturbances of the isochronicity that characterize spiral hairsprings when they deform under the action of gravity.
The solution described in patent application WO2006/045824 uses fixed magnets relatively distant from the mobile magnets on the balance, in order to push these mobile magnets towards the remote resting position. It is thus necessary to use powerful and thus bulky magnets in order to generate a sufficient repulsion force. It has however been observed during tests and simulations in the frame of the invention that a large part of the magnetic flux created by these magnets does not contribute to the function of the balance and escapes towards other components of the movement, whose running it disturbs.